The present invention relates to a cathode arrangement for an electrolytic bath for electrolytic production of pure metals, in particular copper.
In refining raw metals using electrolysis to obtain pure metals, the metal is extracted from an impure anode in an electrolytic bath and deposited onto a cathode in pure form. The impurities remain dissolved in the electrolyte or form the anode sludge.
Different designs are known for the cathodes used in electrolysis. The designs differ mainly in the selection of materials or material combinations of the mounting rail and cathode plate with a view to good electric conductivity, mechanical stability, corrosion resistance, and in order to minimize energy loss. For refining copper, arrangements are known in which the mounting rail is made of a steel-jacketed non-ferrous metal core or has a steel core which is electrolytically copper plated. In the known cathode arrangements, the cathode plate is connected to the current-conducting mounting rail by welding metals of the same type of the mounting rail and cathode plate, such as steel/steel, or by soldering in the case of different metals. Furthermore, U.S. Pat. No. 5,492,609 and European Patent Application 175 395 A1 describe a mounting rail made of copper welded to a cathode plate made of stainless steel.
European Patent Application 301 115 A1 describes a mounting rail having a steel core, which is provided with a thick electrolytic copper plating, the bonding surfaces for the steel cathode plate being subsequently explosion plated with a steel strip to which the steel cathode plate is subsequently welded.
The disadvantage of the known cathode arrangements is their high manufacturing cost. In particular, when steel-reinforced mounting rails are to be provided with thick electrolytic copper plating in order to avoid power losses due to voltage drops, manufacturing is extremely costly and time-consuming.
Welding together different metals such as copper and stainless steel also represents a technical problem. Furthermore, in industrial welding, the workpieces are subjected to considerable warming during the welding process, which may result in longitudinal stresses and deformation of the mounting rail and, in unfavorable cases, in buckling of the cathode plate. For this reason, only discontinuous or spot welds are used in practice, which, however, result in considerable voltage losses at the contact points and in reduced current efficiency.
The object of the present invention is to provide an improved cathode arrangement which achieves minimum power losses at the passage of current from the mounting rail to the cathode plate and which can be manufactured inexpensively.
According to the present invention, this object is achieved with a cathode arrangement in which the mounting rail has an essentially rectangular cross-section and has two parallel flanges extending in the longitudinal direction of the mounting rail on the underside. The cathode plate is accommodated between these two flanges and bonded to the flanges by cold pressure welding. The ends projecting over the cathode plate are designed without flanges at least in the areas reaching the system on the bus bars of the electrolytic bath and have oblique surfaces intersecting in the shape of a wedge at the bottom.
A drawn copper section is preferably used as a mounting rail. The mounting rail may also be designed as a hollow section. The cathode plate, also referred to in the industry as the mother plate, is made of corrosion-resistant stainless steel. In special cases, a cathode plate made of rolled copper may also be used.
The height of the mounting rail is preferably greater than its width. This measure results in a high section modulus. The resulting bending strength has a positive effect on the overall stability of the cathode arrangement, which is advantageous in particular when deposited metal layers are removed (stripped) mechanically.
The flanges designed in one piece on the underside of the mounting rail are used for accommodating and securing the cathode plate. The cathode plate is perpendicular to the mid-section plane of the mounting rail. The flanges are bonded to the cathode plate by cold pressure welding, which is preferably performed by explosion welding. For this purpose, the cathode plate is pressed into the opening between the two flanges, whose external surfaces are coated with an explosive. The explosive is ignited so that a detonation front is formed which propagates over the surface and presses the flanges against the cathode plate. Due to the very high surface pressure, the boundary layers fuse together in the collision zone, forming a firm, full-surface bond having very good current-conducting properties from the contact surfaces of the flanges to the cathode plate. The full-surface metal bond ensures uniform passage of current over the entire bonding surface of the mounting rail and the cathode plate. Voltage losses at the contact points are minimized and the current efficiency is increased. Due to the type of bond obtained by explosion welding, unacceptable longitudinal stresses due to thermal effects and resulting deformations of the cathode arrangement are also avoided.
No disadvantageous heat is introduced in the bonding zones. Thus no fusion processes from which bonding faults or slag or gas inclusions may result can occur. Consequently, points with increased resistance are eliminated.
The full-surface metallic bond between the mounting rail and the cathode plate also increases the mechanical strength of the cathode arrangement.
The length and height of the flanges-can be determined according to the respective application. The advantage is that, when a cathode plate made of corrosion-resistant stainless steel is used, the copper-free area between the electrolyte surface and the mounting rail can be optimized according to the application. Thus, disadvantageous power losses can be reduced in these areas.
In order to accommodate-the cathode arrangement on the bus bars installed parallel to the electrolytic bath, the mounting rails have a flangeless design and are provided with oblique surfaces intersecting in the shape of a wedge on the underside. Thus the mounting rails are placed on the bus bars located in the central longitudinal plane of the mounting rail, forming a linear contact. The advantage of this installation geometry is a secure and always vertical attachment of the cathode arrangement in the electrolytic bath. This contributes to problem-free electrolysis operation.
The lateral surfaces and the top surface of the mounting rail may have a shaped design. The shaped design contributes to improve heat removal over the mounting rail. Heat removal is facilitated through such an enlarged surface.
Furthermore, recesses may be provided on the mounting rails and/or on the cathode plate. The recesses may be used as lifting aids and facilitate handling of the cathode arrangement according to the present invention during manufacture and operation. Normally the recesses are arranged in the cathode plate below the mounting rail, so that the necessary lifting devices can be engaged there. The recesses are also used as passages for the electrolyte flow.